The embodiment relates to a light emitting device, a method for manufacturing the light emitting device, a light emitting device package, and a lighting system.
An LED (Light Emitting Device) is a compound semiconductor device to convert electrical energy into light energy and can emit lights having various colors by adjusting the compositional ratio of a compound semiconductor.
For example, a nitride semiconductor light emitting device has been spotlighted in development fields of an optical device and a high-power electronic device due to high thermal stability and wide bandgap energy. In particular, blue, green, and ultraviolet light emitting devices including a nitride semiconductor have been commercialized and extensively used.
In addition, when comparing conventional light sources such as a fluorescent lamp, and an incandescent lamp, the nitride semiconductor light emitting device has advantages such as low power consumption, a semi-permanent life span, a rapid response speed, stability, and an eco-friendly property. The application of the nitride semiconductor light emitting device is expanded to a light emitting diode backlight serving as a substitute for a CCFL (Cold Cathode Fluorescence Lamp) constituting a backlight of an LCD (Liquid Crystal Display), a white light emitting diode lightening device serving as a substitute for the fluorescent lamp or the incandescent lamp, a vehicle headlight, and a signal light.
In order to expand the application range of the nitride semiconductor light emitting device, the technology for the high efficiency of the light emitting device must be basically developed.
In the light emitting device according to the related art, when a forward voltage is applied, electrons injected from an N-type GaN based electron injection layer are combined with holes injected from a P-type GaN based hole injection layer, so that energy corresponding to the energy gap between a conduction band and a valance band is radiated. The energy is mainly emitted in the form of heat or light. The light emitting device emits the energy in the form of light.
According to the related art, since holes have effective masses greater than those of the electrons, the mobility of holes are remarkably lower than the mobility of the electrons.
In addition, according to the related art, activated hole concentration is lower than electron concentration.
Therefore, according to the related art, light is emitted mainly from a well layer adjacent to a P-type GaN layer, so that the light emission efficiency is reduced. Accordingly, light characteristic may be degraded.
In addition, according to the related art, low carrier distribution is represented in another well layer except for the well layer of the active layer adjacent to the P-type GaN layer, so that the contribution to the luminous intensity by the recombination of holes and electrons may be lowered.